Chuck with torque limiting mechanism and inclined plane for final tightening

Abstract: A chuck (10) for releasably holding a tool such as a drill bit has a torque limiting coupling (60) in the mechanism which is rotated manually to close the jaws (30) of the chuck on the tool. When the chuck has been tightened on the tool by a certain amount, the torque limiting coupling (60) releases. Thereafter, continued manual rotation of the component which provides the input to the coupling operates a cam (80) and cam follower (70) mechanism which forces the jaws (30) of the chuck into even tighter engagement with the tool. When the chuck is subsequently loosened to release the tool, the cam (80) and cam follower (70) mechanism automatically reset to ready the chuck for reuse.

Description: Background of the Invention This invention relates to chucks for releasably holding tools (e.g., drill bits), and more particularly to such chucks which can be easily and simply operated to very securely hold a tool without the need for a key to tighten the chuck on the tool. Chucks with keys for imparting final tightening torque to the chuck to securely hold a tool are well known. While such chucks have been highly successful, they may have certain disadvantages. For example, the key must be removed from the chuck before the chuck is rotated at high speed (e.g., in a drilling operation). Failure to remove the key may unbalance the chuck when rotated at high speed, or cause the key to be thrown out from the chuck in a radial direction in a possibly unsafe manner. Although the key must thus be frequently removed from the chuck, the key must somehow be kept with the chuck or it may become lost. Because of these disadvantages of keyed chucks, there has been increasing interest in recent years in chucks which can be operated by hand without the need for keys (see, for example, Huff et al. U.S. patent 5,125,673 and Jordan et al. U.S. patent 5,215,317 on which is based the preamble of claim 1). Some of these keyless chucks have been highly successful, but there is always room for further improvement. To be acceptable a chuck must be able to hold a tool very securely. Chuck jaws with relatively fine threads serve this objective because fine threads give increased mechanical advantage. However, fine threads make a chuck relatively slow to operate, thereby making the chuck objectionable or even unacceptable to some users. A chuck should also be as simple and easy to operate as possible. For example, it is preferable for the operator to be able to use a single, simple type of motion to tighten or loosen the chuck. The chuck should also reset reliably and automatically after each use so that no additional resetting operation is required from the operator. In view of the foregoing, it is an object of this invention to provide improved chucks. It is another object of this invention to provide manually operable, keyless chucks which do not require especially fine jaw threads to hold a tool very securely, indeed more securely than conventional keyless chucks with fine threads. It is still another object of this invention to provide manually operable, keyless chucks which require the operator to perform only a single, straightforward motion to tighten or loosen the chuck, and which automatically reset after each use in a highly reliable manner. Summary of the Invention These and other objects of the invention are accomplished by a chuck comprising the features of claim 1. It is provided a chuck with a torque limiting mechanism between (1) the chuck component (typically a sleeve) which is manually rotated to tighten the chuck on a tool and (2) the chuck component (typically a nut) which is rotated by the sleeve to advance the jaws of the chuck to grip the tool. When the jaws have been tightened on a tool to a predetermined degree, the resistance to further tightening causes the torque limiting mechanism to release. This allows the sleeve to rotate relative to the nut. The above-described initial tightening of the jaws on the tool also compresses a plurality of rolling cam follower elements (e.g., ball bearings) between a proximal-facing surface of the nut and a distal facing surface which rotates with the sleeve. When the sleeve rotates relative to the nut, the cam follower elements roll along segments of the surfaces between which the cam follower elements are compressed. These segments on at least one of the surfaces are inclined toward the other surface in the direction in which the cam follower elements roll so that the cam follower elements force the nut axially forward relative to the body of the chuck as the cam follower elements roll. This forward motion of the nut forces the jaws farther forward, thereby providing final tightening of the chuck jaws on the tool. When the chuck is again loosened, the cam follower elements are no longer axially compressed between the surfaces along which they roll as described above. A relatively light spring is therefore effective to automatically restore the cam follower elements to their initial positions relative to the inclined surface segments along which they roll. Further features of embodiments of the invention, their nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments. Brief Description of the Drawings FIG. 1 is an elevational view, partly in section, of an illustrative chuck constructed in accordance with the principles of this invention. FIG. 2 is a partial sectional view taken along the line 2-2 in FIG. 1. FIG. 3 is an elevational view of one part of the chuck of FIG. 1 taken in the direction of arrows 3 in FIG. 1. FIG. 4 is a partial sectional view taken along the line 4-4 in FIG. 1. Detailed Description of the Preferred Embodiments As shown in FIG. 1, a chuck 10 constructed in accordance with the principles of this invention has a main body 20 with a central longitudinal bore 22 and three subsidiary bores 24 spaced equidistantly from one another around the central longitudinal axis 12 of the chuck. (Only one of bores 24 is visible in FIG. 1.) The proximal (right-most) end of bore 22 is adapted to receive a driver for the chuck (e.g., the end of the shaft of a manual or powered drill). Bores 24 are inclined toward one another in the distal direction (toward the left) and communicate with the distal portion of bore 22. A longitudinal jaw 30 is disposed in each of bores 24. Each of jaws 30 is reciprocable along its longitudinal axis 32. Jaws 30 are reciprocated by nut 40, which is rotatably mounted on body 20 concentric with axis 12 and threadedly engaged with each of jaws 30. Rotation of nut 40 relative to body 20 therefore causes jaws 30 to move in unison, either toward or away from axis 12, depending on the direction of rotation of the nut. Nut 40 is rotated by rotation of annular front sleeve 50 which (like nut 40) is rotatably mounted on body 20 concentric with axis 12. In general, torque is transmitted from sleeve 50 to nut 40 by ring 60 which is disposed between elements 40 and 50 concentric with axis 12. The construction and operation of ring 60 are described in more detail below. Behind nut 40 (in the proximal direction) is a plurality of ball bearings 70 spaced from one another in an annular array concentric with axis 12 by being disposed in similarly spaced apertures in cage ring 72 (see also FIG. 4). In the particular embodiment shown in the drawings there are four balls 70 equally spaced from one another around axis 12. Behind ball bearings 70 (again in the proximal direction) is an annular cam ring 80 which is concentric with axis 12. Cam ring 80, which is another part that is described in more detail below, is constrained to rotate with sleeve 50 at all times by lugs 52 on sleeve 50 projecting radially inward into mating notches 82 (FIG. 3) in cam ring 80. Behind cam ring 80 (in the proximal direction) is another ball bearing structure including a plurality of ball bearings 90 spaced from one another in an annular array concentric with axis 12 by cage ring 92. (Cage ring 92 is optional and can be omitted if desired.) In the proximal direction ball bearings 90 bear on annular bearing race 100 on body 20. A rear sleeve 110 is secured to the rear of body 20. Nose piece 120 is pressed onto the distal end of body 20 and thereby holds elements such as 40, 50, and 60 on body 20. However, limited motion of nut 40 parallel to axis 12 is permitted. The construction of ring 60 and associated parts is shown in more detail in FIG. 2. Ring 60 has a pair of diametrically opposite, radially and axially extending lugs 62, each of which projects radially inward into a mating axially extending channel 42 in nut 40. Nut 40 and ring 60 are thereby constrained to rotate with one another at all times. Ring 60 also has a pair of diametrically opposite, radially and axially extending lugs 64 which project radially outward from its outer surface. Each of lugs 64 has a substantially radial face 64b and a generally opposite inclined face 64a. Radially inside each of lugs 64 ring 60 has a circumferentially and axially extending aperture 66 which allows the adjacent lug 64 to move radially inward under certain conditions as described below. Lugs 64 on ring 60 interdigitate with radially and axially extending lugs 54 on sleeve 50. Lugs 54 are diametrically opposite one another and project radially inward from the sleeve. Like lugs 64, each of lugs 54 has a substantially radial face 54b and a generally opposite inclined face 54a. When sleeve 50 is rotated in the direction indicated by arrow 56 in FIG. 2 (which is the direction of sleeve rotation required to tighten jaws 30 on a tool), sleeve 50 can rotate relative to nut 40 until the inclined surfaces 54a of lugs 54 contact the inclined surfaces 64a of lugs 64. Thereafter, continued rotation of sleeve 50 in direction 56 causes ring 60 and therefore nut 40 to rotate in direction 56. This causes jaws 30 to move in the distal direction until the tool is gripped by the jaws. When jaws 30 contact the tool, it becomes increasing difficult to continue to rotate nut 40 in direction 56 as the tool gripping force exerted by the jaws increases. It should also be noted that another consequence of the gripping force exerted by jaws 30 on the tool is a reaction force which causes nut 40 to move in the proximal direction and apply a compressive force to balls 70, cam ring 80, and balls 90. When the manual torque which must be applied to sleeve 50 to continue to rotate nut 40 in direction 56 reaches a predetermined threshold torque, ring 60 flexes inwardly in the vicinity of lugs 64 and apertures 66, thereby allowing each of lugs 54 to the pass the lug 64 with which it was formerly in contact. The structure thus described therefore acts as a detent-type torque limiting mechanism. When the detent of this torque limiting mechanism releases, sleeve 50 can continue to rotate in direction 56 without further rotating ring 60 or nut 40. Cam ring 80, however, continues to rotate in direction 56. And because balls 70 have been compressed between nut 40 and cam ring 80, balls 70 begin to roll along the mutually opposing faces of non-rotating nut 40 and rotating cam ring 80. As balls 70 thus roll, they carry cage ring 72 with them. In particular, it will be noted that during this phase of the operation, cage ring 72 rotates about axis 12 in direction 56 at one-half the speed at which sleeve 50 and cam ring 80 are rotating. Springs 130, which as best seen in FIG. 4 extend between sleeve 50 and cage ring 72, are stretched (i.e., placed in increasing tension) by this rotation of sleeve 50 relative to cage ring 72. As shown in FIG. 3, the surface of cam ring 80 along which balls 70 roll as described above has four arcuate channels 84 spaced from one another around the cam ring. Each of balls 70 rolls in a respective one of channels 84. These channels have cross sections which are concave to complement the convex outer surfaces of balls 70. Each of channels 84 becomes gradually shallower in the direction opposite direction 56. Accordingly, as cam ring 80 rotates relative to nut 40 in direction 56, each ball rolls from the deeper end 84a of the associated channel toward the shallower end 84b of that channel. Cam ring 80 thereby forces balls 70 to move in the distal direction. Balls 70 in turn force nut 40 and jaws 30 to move in the distal direction, thereby significantly tightening the grip of jaws 30 on the tool being held by the chuck. The extreme shallow end 84b of each channel 84 may be slightly deeper than the immediately adjacent portion of that channel so that the associated ball 70 has a tendency to remain at the shallow end of the channel until the chuck is deliberately loosened by turning sleeve 50 opposite to direction 56 as described in detail below. From the foregoing it will be seen that the bottom of each channel 84 is a ramp, inclined plane, or cam surface, with the associated ball 70 as a rolling follower for transmitting its axial motion as a follower to nut 40 and therefore to jaws 30. The slope of each channel 84 is extremely gradual, so that very large mechanical advantage is developed from the rotation of sleeve 50 relative to nut 40 during operation of cam ring 80 in the manner just described. It will be noted that each channel 84 subtends an angle of about 700. Sleeve 50 therefore rotates in direction 56 through an angle of about 140° in order to roll balls 70 from the deeper ends 84a of channels 84 to the shallower ends 84b of the channels. Because lugs 54 are about 180° apart on sleeve 50 and lugs 64 are about 180° apart on ring 60, after lugs 54 and 64 pass one another to initiate the rolling of balls 70, the balls reach the shallow ends 84b of channels 84 before lugs 54 re-engage lugs 64. When it is desired to loosen the chuck and remove the tool held by jaws 30, sleeve 50 is rotated opposite to direction 56. This causes balls 70 to roll back from the shallow ends 84b of channels 84 to the deeper ends 84a of those channels, thereby relieving some of the pressure of jaws 30 on the tool. As balls 70 approach the deeper ends of channels 84, the radial faces 54b of lugs 54 come into contact with the radial faces 64b of lugs 64. As a result of this contact, continued rotation of sleeve 50 opposite to direction 56 causes ring 60 and nut 40 to rotate opposite to direction 56. This retracts jaws 30 and releases the tool from the chuck. When the pressure of the jaws on the tool is sufficiently relieved, elements 70, 80, and 90 are no longer compressed between nut 40 and bearing race 100. This allows springs 130 (acting in tension in the circumferential direction between sleeve 50 and ball cage 72) to automatically rotate ball cage 72 (if necessary) relative to elements 50 and 80 so that balls 70 return to the deeper ends 84a of channels 84. The chuck is thus fully and reliably reset after each use so that it is always ready for the next use. Because springs 130 are only required to rotate cage ring 72 when there is substantially no compressive force on balls 70, the force of springs 130 can be relatively small so that even when they are fully stretched, they do not significantly tend to loosen the tightened chuck by strongly urging balls 70 to roll from the shallow ends 84b of channels 84 to the deeper ends 84a of those channels. When it is next desired to clamp a tool in the chuck, sleeve 50 is again rotated in direction 56. The first nearly 180° of this rotation may be required to cause the inclined surfaces 54a of lugs 54 to re-engage the inclined surfaces 64a of lugs 64. (Balls 70 do not roll during this relative rotation between sleeve 50 and nut 40 because balls 70 are not then compressed between the nut and ring 80.) Thereafter, continued rotation of sleeve 50 in direction 56 rotates ring 60 and nut 40 in the same direction, thereby moving jaws 30 in the distal direction toward the tool to be clamped. Operation of the chuck then continues as first described above. Among the advantages of chuck 10 is that sleeve 50 is substantially decoupled from nut 40 while the chuck is tightened on a tool. The inertia of nut 40 is thereby reduced. This enhances the ability of the chuck to remain tight by resisting vibration and accelerations in the longitudinal and circumferential directions. Although the various components of chuck 10 can be made of any of many suitable materials, particularly preferred materials for sleeve 50 and ring 60 are nylon and acetal, respectively. It will be understood that the foregoing is only illustrative of the principles of this invention, and that various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention. For example, the numbers of such components as lugs 54, lugs 64, balls 70, and channels 84 can be varied as desired. If the chuck is mounted on a tool having a spindle lock, sleeve 50 can be extended farther to the rear and separate rear sleeve 110 can be eliminated. As another example of possible modifications, channels 84 can be moved from the distal surface of ring 80 to the opposite proximal-facing surface of nut 40, or such inclined channels can be provided on both of these surfaces. Radially extending roller bearings may be used in place of balls 70, with appropriate modification of the shape of channels 84 to accept such rollers rather than balls. Instead of having lugs 64 deflect inwardly to pass lugs 54, lugs 54 could deflect outwardly to permit such passing. Instead of having stop surfaces 54b and 64b which are positioned to engage one another before sleeve 50 is rotated all the way back to the position in which the associated inclined surfaces 54a and 64a are facing one another, lugs 54 and 64 could be shaped so that they very easily pass one another when sleeve 50 is rotated in the loosening direction, and other stop surfaces (like surfaces 54b and 64b but with at least different angular positions and possibly also different axial positions) could then engage one another to prevent further rotation of sleeve 50 opposite to direction 56 without similar chuck-loosening rotation of ring 60 and nut 40. Indeed, these alternative stop surfaces could be located on elements other than 50 and 60 if desired. As still another example of possible modifications, the torque limiting operation provided between sleeve 50 and ring 60 could alternatively be provided between ring 60 and nut 40. Instead of the releasable detent-type torque limiting mechanism shown in the drawings, the torque limiting mechanism could be of the friction type. Such a friction-type torque limiting mechanism takes advantage of the fact that static friction between two surfaces is greater than sliding friction between those surfaces under otherwise similar conditions. Thus static friction between elements 50 and 60 would be used to transmit torque from sleeve 50 to ring 60 until a threshold torque was reached, at which point reduced sliding friction would allow sleeve 50 to rotate relative to ring 60. It will be noted that the torque limiting mechanisms employed in accordance with this invention are preferably "passive" in the sense that they do not store energy to any significant degree. This is true of both the depicted releasable detent-type torque limiting mechanism and the alternative friction-type torque limiting mechanism described immediately above. These passive torque limiting mechanisms transmit torque applied to them, but unlike a spring, for example, they do not significantly store energy which could cause the chuck to loosen after it has been tightened on a tool and while the tool is being used.

Claims: A chuck (10) for releasably gripping a tool and comprising: a main body (20); a plurality of longitudinal tool-gripping jaws (30) mounted for movement relative to said main body (20), each of said jaws (30) being movable relative to said main body parallel to the longitudinal axis of that jaw, the longitudinal axes of said jaws (30) being synclinal in the distal direction along said body (20); a nut (40) rotatably mounted on said body (20), said nut (40) being also mounted for limited axial motion relative to said body parallel to said distal direction, said nut (40) being threadedly engaged with each of said jaws (30) for causing said jaws to move parallel to their longitudinal axes when said nut (40) is rotated relative to said body (20) or when said nut (40) is moved axially relative to said body (20) parallel to said distal direction; a sleeve (50) rotatably mounted on said body (20); a plurality of rolling cam follower elements (70) disposed between a substantially proximal-facing first surface of said nut (40) and a substantially distal-facing second surface that rotates relative to said body (20) with said sleeve (50), said cam follower elements (70) being axially compressed between said first and second surfaces only after said jaws (30) have begun to grip a tool and said nut (40) moves relative to said body (20) in the proximal direction in reaction to the tool-gripping force applied to the tool by said jaws (20); and means (130) for resiliently urging each of said cam follower elements (70) to automatically return to its initial position relative to at least one of said first and second surfaces when said cam follower elements (70) are not compressed between said first and second surfaces; characterised in that a torque limiting coupling (60) is provided, and operatively connected between said sleeve (50) and said nut (40) for causing said nut (40) to rotate relative to said body (20) with said sleeve (50) in a jaw-tightening direction until said jaws (30) have begun to grip the tool and more than a predetermined threshold torque must be applied to said sleeve (50) to continue to rotate said nut (40) in said jaw-tightening direction, after which said torque limiting coupling (60) releases so that said sleeve (50) can continue to rotate in said jaw-tightening direction with at least substantially reduced transmission of torque from said sleeve (50) to said nut (40) and therefore without further rotation of said nut (40) in said jaw-tightening direction; each of said cam follower elements (70) rolling, from initial positions relative to said first and second surfaces, along an arcuate segment of each of said first and second surfaces when said cam follower elements (70) are compressed between said first and second surfaces and after said torque limiting coupling has released and said sleeve (50) continues to rotate in said jaw-tightening direction relative to said nut (40), at least one of said segments along which each of said cam follower elements (70) rolls being inclined toward the other of the segments along which that cam follower element rolls in the direction in which that cam follower element rolls so that said cam follower elements (70) force said nut (40) to move in said distal direction relative to said body (20), thereby further tightening said jaws 30 on the tool. The apparatus defined in claim 1 wherein said cam follower elements (70) are connected to one another by an annular cage ring (72) which is disposed circumferentially around said body (20) and which is rotatable relative to said body (20) and relative to said first and second surfaces, and wherein said means for resiliently urging comprises a spring (130) which acts in the circumferential direction between said cage ring (72) and at least one of said first and second surfaces. The apparatus defined in claim 1 or claim 2 wherein said torque limiting coupling (60) comprises a releasable detent coupling (54,64) between said sleeve (50) and said nut (40), said releasable detent coupling transmitting torque from said sleeve (50) to said nut (40) when said sleeve (50) is rotated in said jaw-tightening direction until said torque reaches said threshold torque, after which said releasable detent coupling (54,64) releases and transmits substantially no torque from said sleeve (50) to said nut (40) during continued rotation of said sleeve (50) in said jaw-tightening direction. The apparatus defined in any preceding claim wherein each of said cam follower elements (70) is a ball. The apparatus defined in claim 4 wherein said at least one of said segments along which each of said elements rolls is a channel (84) having a convex cross section for receiving a portion of the surface of a ball. The apparatus defined in claim 5 wherein each of said channels (84) becomes progressively shallower in the direction in which the ball in said channel rolls. The apparatus defined in any preceding claim further comprising: stop means (54b, 64b) operatively coupled between said sleeve (50) and said nut (40) for preventing said sleeve (50) from rotating by more than a predetermined amount relative to said nut (40) in a direction opposite to said jaw-tightening direction. The apparatus defined in any preceding claim wherein each of said segments along which said cam follower elements (70) roll is an arc substantially concentric with an axis about which said nut (40) concentrically rotates.

Inventors: HUFF ROBERT O, SHADECK LOUIS M, HUFF, ROBERT O., SHADECK, LOUIS M.
Applicants: POWER TOOL HOLDERS INC, POWER TOOL HOLDERS INCORPORATED
Application year: 1994
Main classification: B23B31
IPC codes: B23B31, F16D7